In our previous work, we isolated a diploid rat liver, hepatocyte cell culture and characterized its response to aflatoxin B1. We also succeeded in transforming this culture which, for the first time, demonstrated the transformation by aflatoxin B1, of a cell culture derived from the in vivo target tissue. In this project we propose to continue the characterization of the normal and transformed hepatocyte culture by morphological,karyological and biochemical analyses using control and toxin-treated cultures which had been sequentially stored in liquid nitrogen during the transformation process. We propose also to study the surprising differences in RNA biosynthesis between the diploid and heteroploid cultures used. We also propose to study the interesting morphological variants found in long term normal cultures and relate these to similar variants which are present in toxin transformed cultures and in the ascites tumors derived from them.